The present invention relates to improvments in the processability of polyamides such as nylon polymers and more particularly to lowering the temperature at which nylon compositions undergo a reversible solid to liquid phase change.
Nylon is the generic name for a family of polyamide polymers characterized by the presence of the amide group--CONH. The utility of nylon compositions and products are well known with everyday examples including usage in brushes, tires, etc., as synthetic fibers, plastics, films and molding resins.
It is known that certain compositions may be added to nylon to aid in plasticization and in general as processing aids. Various polar, hydrogen-bonding plasticizers have been added to nylon compositions as flow aids to retard degradation of the resin and speed up processing. Commonly used in this regard is N-ethyl-(o,p)-toluenesulfonamide. Other compounds including other sulfonamides have also been found useful. See, "Plasticizers," Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 18, 3rd Ed., 157-160 (J. Wiley & Sons, Inc., 1982). Nylon is also known to be plasticized by traces of water, anhydrous ammonia, and other polar solvents.
Generally, plasticizers are incorporated into a material to increase its workability, flexibility, or distensibility. The addition of a plasticizer may lower the melt viscosity, second-order transition temperature or the elastic modulus of the plastic. For a platicizer to be effective with any polymeric material, the plasticizer and polymeric material must be intimately mixed. This is typically accomplished by heating until one dissolves in the other or by dissolving in a solvent. Plasticizers may sometimes be utilized as processing aids to lower the processing temperature without altering the usefulness of the final product. See generally, "Plasticizers," supra, at 111-177. Plasticizers are also added to crystalline nylon resins in small amounts to improve such properties as flexibility, toughness, adhesion, dye penetration, etc.
Lithium halides such as lithium chloride have also been used in processes to lower the melting point of polyamides formed from dry lactams having 4 to 12 carbons atoms. See, e.g., U.S. Pat. No. 4,092,301 and the book Fiber-forming Polymers (Recent Advances), pp. 157-159 (Noyes Data Corp., 1980). A disadvantage of these known processes is their failure to lower the melting point temperature of certain polyamides (notably nylon-3 compositions) and still maintain sufficient thermal stability to prevent decomposition.